Flotation processes have been developing over a period of more than 100 years, and various designs are in existence. One such system is the conventional mechanical cell employing an impeller located within a tank. A gas is introduced and dispersed through the impeller in order to generate bubbles to which the hydrophobic particles to be concentrated will adhere (see C. C. Harris, 1976). These mechanical cells continue to be the machines most widely used at the present time.
However, recent years have seen the introduction into the ore industry of machines generically known as "pneumatics," which had already been used in chemical processes and for waste water treatment (see Clarke & Wilson, 1983). In these machines the mixing of the gas and slurry takes place by means of injection nozzles. The most common of these devices are those known as columns and those of the Flotaire type (see K. V. S. Sastry, 1988). These have not yet been used in the ore industry on a large scale, however, due to difficulties in controlling their operation.
Finally, another type of machine has been developed recently, the length of which is shorter than that of columns. In these machines, the slurry is injected under pressure (see G. J. Jameson, 1988).